Thread: Thicknesser blade types

Think along the lines of handplaning. If the material is nicely straight grained, a hand plane working working with the sole parallel to the edge should produce a decent finish if you plane in the right direction, plane in the wrong direction and it will tend to dig in and cause the surface to chip out. If the grain starts to get a bit cranky, i.e run in various directions, its harder to get the smooth finish, so as well as planing in the right direction, you might skew the plane to change the angle that the blade is approaching the fibres to obtain best results. If the grain structure is very cranky, i.e going in all directions, then you might need to resort to using a hand scraper or scraper plane to achieve a good finish.

With a thicknesser, the situation is similar, a straight blade head is the equivalent of 2, 3, or 4 plane blades working along the timber in succession. If you get minor chip out, you can skew the work relative to the head as you feed it into the machine to tweak the blade approach angle, just as you might skew a handplane. There are limits though as the material crabs going through the machine and the width of the cutter head and length/width of the work will limit the amount that you can skew it without it colliding with the head side frames during passage.

Some machines were made with long helical blades that spiralled part way around the head, but the blades need to be thin to form the spiral and may not be rigid enough to do a good job. They are also a nightmare to sharpen as they need to mounted in a jig that exactly mimics the cutter head to grind them accurately, or alternative disposable.

The modern approach is to use indexible carbide cutter inserts arranged in a segmented helical pattern around the head, secured by screws. By combining multiple rows of inserts in a moderate spherical layout, the benefits if the continuous helical blades are obtained without the issues associated with sharpening or replacing the blades. The inserts used generally have four cutting edges and once the first edge becomes worn, the insert can be released by unscrewing, rotated 90 degrees to a fresh edge, and refastened. If a nail or similar causes a chip at one point accross the head width, this can be fixed quickly by indexing the inserts at that position, without needing to touch the rest. Apart from ensuring that the head under the insert is free of dust or residue, there is no complex blade setting process required, as is the case with a straight blade unit. Pricewise, the machines are dearer because of the machining required to accurately produce a non adjustable head, and the cost of the multiple inserts used. The inserts are carbide and harder than the commonly used HSS blades in straight heads, so retain their edge much longer if not damaged by metal impact. They also provide four cutting edges, so a set might last the equivalent of 10-15 HSS blade sharpenings/replacements with care. A lot of the non industrial HSS bladed machines use thin narrow blades that cannot be sharpened or can only be sharpened a couple of times before becoming too small for effective sharpening and use. Typical cost for replacement 15inch HSS blades can be $100 a pair, so the inserts work out cheaper over time.

When using straight HSS machines, you get interupted cuts as a blade leaves the material before the next blade enters it. This is a noisy process. With a segmented helical head, there are always inserts in the material, and inserts enter and leave the work in a progressive fashion. This results in quieter operation, important in industrial settings.

From your previous posts, you appear interested in a thicky sub $500, but I haven't come accross any in that price range that use segmented heads, but hope that the general info might be usefull for you.

My full review of the helical head here: https://www.woodworkforums.com/f154/u...4/#post1657745

Originally Posted by malb

Think along the lines of handplaning. If the material is nicely straight grained, a hand plane working working with the sole parallel to the edge should produce a decent finish if you plane in the right direction, plane in the wrong direction and it will tend to dig in and cause the surface to chip out. If the grain starts to get a bit cranky, i.e run in various directions, its harder to get the smooth finish, so as well as planing in the right direction, you might skew the plane to change the angle that the blade is approaching the fibres to obtain best results. If the grain structure is very cranky, i.e going in all directions, then you might need to resort to using a hand scraper or scraper plane to achieve a good finish.

With a thicknesser, the situation is similar, a straight blade head is the equivalent of 2, 3, or 4 plane blades working along the timber in succession. If you get minor chip out, you can skew the work relative to the head as you feed it into the machine to tweak the blade approach angle, just as you might skew a handplane. There are limits though as the material crabs going through the machine and the width of the cutter head and length/width of the work will limit the amount that you can skew it without it colliding with the head side frames during passage.

Some machines were made with long helical blades that spiralled part way around the head, but the blades need to be thin to form the spiral and may not be rigid enough to do a good job. They are also a nightmare to sharpen as they need to mounted in a jig that exactly mimics the cutter head to grind them accurately, or alternative disposable.

The modern approach is to use indexible carbide cutter inserts arranged in a segmented helical pattern around the head, secured by screws. By combining multiple rows of inserts in a moderate spherical layout, the benefits if the continuous helical blades are obtained without the issues associated with sharpening or replacing the blades. The inserts used generally have four cutting edges and once the first edge becomes worn, the insert can be released by unscrewing, rotated 90 degrees to a fresh edge, and refastened. If a nail or similar causes a chip at one point accross the head width, this can be fixed quickly by indexing the inserts at that position, without needing to touch the rest. Apart from ensuring that the head under the insert is free of dust or residue, there is no complex blade setting process required, as is the case with a straight blade unit. Pricewise, the machines are dearer because of the machining required to accurately produce a non adjustable head, and the cost of the multiple inserts used. The inserts are carbide and harder than the commonly used HSS blades in straight heads, so retain their edge much longer if not damaged by metal impact. They also provide four cutting edges, so a set might last the equivalent of 10-15 HSS blade sharpenings/replacements with care. A lot of the non industrial HSS bladed machines use thin narrow blades that cannot be sharpened or can only be sharpened a couple of times before becoming too small for effective sharpening and use. Typical cost for replacement 15inch HSS blades can be $100 a pair, so the inserts work out cheaper over time.

When using straight HSS machines, you get interupted cuts as a blade leaves the material before the next blade enters it. This is a noisy process. With a segmented helical head, there are always inserts in the material, and inserts enter and leave the work in a progressive fashion. This results in quieter operation, important in industrial settings.

From your previous posts, you appear interested in a thicky sub $500, but I haven't come accross any in that price range that use segmented heads, but hope that the general info might be usefull for you.

Thanks for the reply.

I am interested sub 500 but the budget seems to be stretching as people continually recommend the carbatec 13 spiral.